Is there a way to simulate custom grid heatmap with various intensity

What I’m trying to do

I am trying to visualize muscle soreness/recovery on my current gym tracker/logger workout (you can check out here but still under development as you see this thread)

basically it should creates a basic render of muscles position in heatmap, and each recent exercises on the targeted muscles will get highlighted (simulate the soreness/muscles hit), and will be slowly reduce the soreness across the span of 7 days.

and i know it will never be accurate, but i think it will be nice to see how we did in the past 7 days, group-wise, and start workout routine that is on the other muscle groups just by looking at the heatmap.

Things I have tried

I have tried to search around how to create a custom grid but i still don’t really get the concepts and how to implement it to my gym log.